set numpy requirement for aarch64 and py3.9 (#43722)

It is stated in this file on line 13 that `# Aarch64(Python 3.9 requirements are the same as AMD64)`
However, the python 3.9 numpy requirement is excluding `aarch64`, therefore there is no `aarch64` numpy requirement defined at all for py3.9.
When one tries to build pandas from source on `aarch64` with py3.9, there is no matching numpy found and therefore the build fails.

This commit sets the numpy version requirement for `aarch64` on py3.9 the same as amd64 as stated.

Author: aptalca

pyproject.toml

@@ -9,7 +9,7 @@ requires = [
     # Copied from https://github.com/scipy/scipy/blob/master/pyproject.toml (which is also licensed under BSD)
     "numpy==1.17.3; python_version=='3.7' and (platform_machine!='arm64' or platform_system!='Darwin') and platform_machine!='aarch64'",
     "numpy==1.18.3; python_version=='3.8' and (platform_machine!='arm64' or platform_system!='Darwin') and platform_machine!='aarch64'",
-    "numpy==1.19.3; python_version>='3.9' and (platform_machine!='arm64' or platform_system!='Darwin') and platform_machine!='aarch64'",
+    "numpy==1.19.3; python_version>='3.9' and (platform_machine!='arm64' or platform_system!='Darwin')",
     # Aarch64(Python 3.9 requirements are the same as AMD64)
     "numpy==1.19.2; python_version=='3.7' and platform_machine=='aarch64'",
     "numpy==1.19.2; python_version=='3.8' and platform_machine=='aarch64'",